The present invention relates generally to a method and an apparatus for continuously treating molten metal, and more particularly to such method and apparatus which are adapted to effect a continuous supply of determinate treating agents to a flowing mass of molten metal and thereby treat the molten metal through contact of the agents with the melt, in an effective manner irrespective of an amount of the melt to be treated.
There has been known in the art a method of improving the structure of cast products as in the form of an ingot, by adding a treating agent or agents (additives) to a molten metal from which the products are obtained by casting. For example, it is well known to inoculate a molten cast iron, or spheroidize the same for providing spheroidal or nodular graphite in the cast iron. To obtain such nodular graphite, various spheroidizing methods have been proposed. In a commonly employed spheroidizing method, predetermined spheroidizing agents such as Mg, RE, Ca, and other metals or their alloys are introduced into a ladle for reaction of a molten metal in the ladle with such treating metals or alloys, and the spheroidized melt is poured into a casting mold whereby a product is obtained in the form of nodular or spheroidal graphite cast iron.
However, such known spheroidizing method which requires a treating process within a ladle, makes it difficult to automate a process of pouring the molten metal into a mold through suitable automatic pouring equipment. Another potential problem associated with the known method resides in a loss of expensive treating agents such as Mg and RE because of their chronological change in properties during a time lapse in the range of several seconds to ten and several minutes, which time lapse is inevitable to transfer the spheroidized molten metal from the ladle to the casting mold. The requirement for the above transfer of the molten metal from the ladle to the mold causes environmental problems due to production of a large volume of white smoke and splashing of the melt, as well as makes the operation cumbersome and dangerous. Further, the contact of the molten metal with ambient air will possibly induce development of slags in a large amount, and consequently reduces efficiency of the spheroidizing agents and have an adverse effect on the quality of the end products.
In recent years, a so-called "in-mold treating process" has been attracting attention of the industry as one of spheroidizing methods. In such process, a required spheroidizing agent is accommodated in a reaction chamber formed in a casting mold, and a mass of molten cast iron is introduced into the reaction chamber for causing contact and reaction of the cast iron with the spheroidizing agent. The molten iron thus treated is then directed through a runner to a mold cavity formed in the other part of the casting mold. In this in-mold treating process, however, the molten metal once poured into the reaction chamber is introduced into the mold cavity only after the molten metal has overflowed the reaction chamber, and therefore the last volume of the molten metal is necessarily left within the reaction chamber. This will reduce the yield of the molten metal in the form of cast products, resulting in an increase in the casting cost of the products. In addition to this critical drawback, the process has further problems in connection with the casting mold which has a reaction chamber as stated above, that is, the mold must be large-sized and complicated in construction due to provision of such reaction chamber therein.
While the above indicated problems are all concerned with a spheroidizing process as applied to a molten cast iron, similar problems are inherent in other treatments of molten metal including an inoculation treatment thereof.
In summary, the prior methods for treating molten metal use a batch treatment process wherein the treatment is conducted in a vessel such as a ladle of a suitable type of a size depending upon the size of a product to be cast, or in a reaction chamber of a suitable size formed in a casting mold. It is found very much difficult to change the amount of treating agents in such treating vessel or chamber after the delivery of a molten metal is started. Thus, the treating agents may be insufficient in amount, or used in excess.